Respect British spelling also in arguments

Summary: These are the errors I really do.

Test Plan:
  $ arc diff --no-lint
  (Assuming '--no-lint' is the British spelling of '--nolint'.)
  $ arc diff --reviewer a
  (Assuming '--reviewer' is the British spelling of '--reviewers'.)

New unit test.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5185